Anticorrosive grindstone

ABSTRACT

A METHOD FOR PRODUCING A GRINDSTONE CHARACTERIZED BY MOLDING AN EPOXY RESIN BINDER WITH A HARDENING AGENT, ACTIVE SULPHUR AND SODIUM NITRITE. THE NOVEL GRINDSTONE IS USED TO PREVENT RUST AND UNEVEN FINISHING OF A TREATED METAL SURFACE. THE GRINDSTONE REPLENISHES THE LOSS DUE TO HYDROLYSIS OF THE GRINDING SOLUTION, THEREBY ENABLING THE GRINDING SOLUTION TO MAINTAIN ITS LUBRICATING AND ANTICORROSIVE PROPERTIES.

United States Patent O fice US. Cl. 51-298 6 Claims ABSTRACT OF THEDISCLOSURE A method for producing a grindstone characterized by moldingan epoxy resin binder with a hardening agent, active sulphur and sodiumnitrite. The novel grindstone is used to prevent rust and unevenfinishing of a treated metal surface. The grindstone replenishes theloss due to hydrolysis of the grinding solution, thereby enabling thegrinding solution to maintain its lubricating and anticorrosiveproperties.

This application is a continuation-in-part of copending application Ser.No. 650,662, filed June 22, 1967 and now abandoned.

BACKGROUND OF THE INVENTION The object of the present invention consistsof preparing a grindstone with lubricating anticorrosive properties soas to prevent rust on the treated metal surface by uniformlydistributing powerful lubricating anti-corrosive materials in thegrindstone to be used for grinding metal. The specific lubricatinganticorrosives which are contained in the grindstone gradually dissolveinto the grinding solution and act upon the surface of the metal to beground as the grinding operation proceeds and as the grindstone isabraded. The mixed lubricating anticorrosives are effective throughoutthe entire use of the grindstone, displaying a distinguishedeffectiveness in obtaining sufiicient grinding and in preventing rust onthe metal products to be treated. The present invention relates to themethod for producing such a lubricating and anticorrosive grindstone.

DESCRIPTION OF THE PRIOR ART When metal products are finished in thepresence of a water-soluble grinding solution, there has very oftenoccurred the problem of rust on the finished metal surface. This problemfrequently arises prior to the anticorrosive treatment of the finishedproducts owing to the deterioration and hydrolytic loss of efficiency ofthe grinding solution with lapse of time. To avoid such problems, it isnecessary that the anticorrosive and lubricating properties of thegrinding solution itself should be reinforced and replenished, even whenthe finished articles are exposed to moisture, which is the cause ofrust prior to the anticorrosive treatment. The residual grindingsolution should be powerful enough to form its primary anticorrosivefunction by enveloping the metal surface with a film.

The methods for improving the anticorrosive properties of the grindingsolution have so far been limited to the improvement of the primaryefiiciency of the grinding solution, for example, to make the pH of thesolution higher than 8.5 or to use an ion blocking agent or the like.There has been no method to prevent the loss of etficiency due tohydrolysis of the water soluble grinding solution which is the keysource of the above discussed problems. The rate of hydrolysis ofanticorrosive and lubricating materials in the grinding solution isreferred to as the 3,595,634 Patented July 27, 1971 secondary eificiencyof the solution. Since there has been no method to improve thissecondary efficiency in preventing rust, loss of grinding properties andthe like, a technical bottleneck has remained until broken by thepresent invention. This has been a great disadvantage to the grindingoperation on a mass production system, resulting in a serious hinderanceto industrial advancement.

In the grinding operation of metal, lack of precision in grinding andthe development of rust are serious problems which call for an immediatesolution. Very important in this connection is the fact that thegrinding efiiciency is greatly impaired by hydrolysis arising with thelapse of time irrespective of whether a water soluble grinding solutionis employed or not. The problem of this loss has not been solved nor hasit been fully recognized by those skilled in the art.

Special attention must be paid to the fact that the anticorrosiveproperty of a fresh grinding solution, however excellent it may be, ismerely the function of the primary etficiency of the grinding solution.It must be noted that the important problem is how to minimize the lossof efficiency due to hydrolysis and how to retain this efiiciency. Withrespect to the anticorrosive property of the grinding solution, greatemphasis should be placed upon the secondary eiiiciency, that isresistance to decomposition, in view of the fact that all grindingsolutions are susceptible to hydrolytic loss in the course of use.Consequently, it is clear that the hydrolytic loss of anticorrosiveefliciency is fatal to the precision of the grinding process as well asto the mass production of metal articles.

PARTICULARS OF THE INVENTION The deterioration of the lubricating andanticorrosive efficiency of the water soluble grinding solution has sofar been attributed only to (1) the nature of water used for thedilution of the grinding solution, for instance, the effect of hardwater containing metals, such as calcium and the like and (2) theproblems due to calcium, sulfur, pulverized grindstone and metal wasteresulting from the grinding operation. Consequently wheneverdeterioration of grinding efiiciency arises due to rust or other suchproblems, the only counter-measure taken by the prior art has been toadd fresh grinding solution to compensate for that loss or to replacethe entire solution with fresh material.

It has been considered until the present invention, that thedeterioration of the lubricating and anticorrosive efliciency of thewater soluble grinding solution is due to foreign elements produced inthe course of the grinding operation. In reality, the loss of efficiencyis chiefly due to hydrolysis and it has never been recognized that therewill be no fundamental improvement unless the foregoing disadvantage isavoided.

In the present invention, to remove the aforementioned technicaldefects, a binder having powerful lubricating and anticorrosiveproperties is uniformly distributed in the grindstone, said binderslowly dissolving in the grind ing solution in the course of thegrinding operation, thereby effectively replenishing the efliciency ofthe grinding solution as it is deteriorated by hydrolysis. The bindercomposite will dissolve into the grinding solution throughout the entireperiod of use of the grindstone and problems arising from the loss oflubricating and anticorrosive properties of the grindstone will beprevented. The invention therefore enables the obtention of an excellentgrindstone which can transform the grinding solution into that of anefficient non-degrading type, greatly contributing to the technicaldevelopment of the metal grinding process.

More specifically, abrasives can be chosen from among materials such asAlundum, Carborundum and the like.

An epoxy resin is employed as the binder. The most significant propertyof the epoxy resin consists of the fact that this type of resin can bereadily changed even at room temperature, from a liquid or thermoplasticstate into a solid mass of thermosetting resin characterized bytoughness. This phenomenon of changing the plastic or semiplastic massinto a solid mass is called hardening or curing. A suitable epoxy resinto be employed in the present invention is a diepoxide of theepichlorohydrinbisphenol A type such as Epikote 828 (Shell Chemical)(equivalent weight based on epoxide groups 182-194) having epoxidegroups at both terminal positions of its molecular chain. It exists inthe form of a viscous liquid, its molecular weight being 360 to 560 andits equivalent weight based on epoxide groups being 180 to 260.

For hardening, the addition of a hardening agent (or curing agent) isindispensible. As a hardening agent, a chemical compound which iscapable of readily reacting with epoxide groups is employed. Suchcompounds are primarily amines, secondary amines, dicarbonic acid andits anhydride, and the like. Primary and secondary amines are used mostwidely. Among suitable amines are diethylentriamine, triethylentetramineand the like.

Although the hardening of the epoxy resin begins with the addition ofthe hardening agent, the curing time required largely depends on thetemperature. When an amine is used as a hardening agent, the hardeningmay take place even at room temperature, but the curing time can beremarkably shortened by elevating the temperature. The optimaltemperature for hardening ranges between normal room temperature and 90C. Active sulfur (alpha or sublimed sulfur) is mixed with the amine andsodium nitrite to obtain sodium amine nitrite sulfide, which is in turnmixed with the epoxy resin to obtain a molding agent for the preferredabrasive. The amines and sodium nitrite in essence act as anticorrosiveswhile the sulfur acts as a lubricant. In practice, however, thesecompounds exist in the form of reaction products; the amine nitriteacting as the effective anticorrosive and the amine sulfide as alubricant.

The molding can be affected either at normal temperature or by heating.When sulfur, sodium nitrite and amine in excess of the equivalentquantity of epoxide, are added, the epoxy resin starts a hardeningreaction, and various reactions simultaneously arise from the amine,sulfur and sodium nitrite. For instance, diethylenetri'amine and sulfurreact as follows:

Amine and sodium nitrite react as follows:

resulting in production of the amine sulfide and amine nitrite,respectively. Furthermore, sodiumamine nitrite sulfide is obtainable bymixing active amine sulfide, sodium nitrite and amine nitrite sulfide bymixing amine nitrite and sulfur, the products having a powerfulanticorrosive and lubricating effect. These products display a fargreater anticorrosive property when produced in the presence of epoxyresin, and far greater rust-proof property is obtainable when theanticorrosives, such as amine, sodium nitrite and the like, arecompounded with epoxy resin as compared with the case wherein suchanticorrosives are simply added to the grindstone as ingredientsthereof. Among the suitable epoxy resins is the diepoxide ofepichlorohydrin-bisphenol A type, having epoxide groups at both terminalpositions of its molecular chain. It exists in the form of viscousliquid, its molecular weight being 360-560 and its equivalent weight(based on epoxide groups) being 180-260.

Preferred ranges of epoxy resin are 30 to 50% by weight of the entirecomposition; preferred ranges of amine are 120 to 250% of the equivalentamount of epoxide; preferred ranges of sulfur are 0.3 to 1.0% of theentire composition and preferred ranges of sodium nitrite are 3 to 10%of the entire composition. Preferred molding temperatures are roomtemperature to C. and preferred pressures for molding are 50 to 300kg./cm.

A grindstone of excellent quality is obtainable by mixing and moldingthe foregoing materials, the anticorrosives and hardening materialswhile the epoxy resin hardens, the lubricating and anticorrosivematerials being uniformly distributed throughout the grindstonesimultaneously. If the metal grinding operation is conducted with such agrindstone, the ingredients gradually dissolve into the grindingsolution as the grindstone is abraded, giving the grinding solutionenhanced lubricating and anticorrosive properties. Moreover, as thedissolution continuously occurs throughout the period of use of thegrindstone, problems arising from the deterioration of the efficiency ofthe grinding solution can be prevented, displaying the eifect oftransforming the grinding solution into an efiicient nondegrading type.

The present invention is useful with grinding solutions which degradeeither by hydrolysis or other phenomena. A grinding solution uesful inthe present invention is, for example, one containing sodium nitrite,amine and surfactant. Another suitable solution is, for example, onecontaining amine derivatives. The present invention is most useful withgrinding solutions containing anticorrosive lubricants such as aminesodium nitrite, amine nitrite, and amine sulfides, etc.

The term sodium amine nitrite sulfide denotes a mixture composed of anamine sulfide and sodium nitrite which mixture has both anticorrosiveand lubricating properties.

All percentages set forth herein are by weight.

The preferred embodiments are disclosed hereunder.

EXAMPLE 1 Abrasives: Parts Alundum 1 60 Corundum 1 40 Lubricating andanticorrosive binders? Fluid epoxy resin (Epikote 828 Shell Chemicalequivalent 182-194) 2 Diethylenetriamine 2 15 Sulfur 2 1 Sodium nitrite2 10 1 Admixture 60 parts.

2 Admixturo 40 parts.

The lubricating anticorrosives are fully incorporated, to 40 partsthereof being added 60 parts of the abrasive, the resultant admixturebeing fully incorporated and then granulated, the grains thus obtainedbeing heated at 40 to 80 C. and then molded into a grindstone with apressure of 200 kg./cm.

1 Admixlture 55 parts.

2 Admlxture 45 parts.

The lubricating anticorrosives are fully incorporated, to 55 partsthereof 45 parts of the abrasives being added, the resultant admixturebeing fully incorporated and then granulated, the grains thus obtainedbeing heated at 70 C. and then molded into a grindstone with a pressureof 200 kg./cm.

METAL SURFACE Rust appearing time, Kind of grindstone Grinding solutionmin.

Ordinary grindstone Water D0 Water soluble grinding 70 solution.Anticorroslve grindstone Water 2 120 1 Of the invention.

2 Or more.

What is claimed is:

1. A process for producing a grindstone comprising: (a) preparaing agrindstone composition by admixing (l) epoxy resin30 to 50% by weight ofsaid composition,

(2) a hardening agent for said epoxide selected from the groupconsisting of primary and secondary amines-420 to 250% of the equivalentweight of said epoxide,

(3) sodium nitrite-3 to by weight of said composition,

(4) active sulphur-0.3 to 1% by weight of said composition, (5) abrasivegrainsthe balance of said composition;

(b) molding said grindstone composition into a grindstone attemperatures between room temperature and 90 C. under a pressure of to300 kg./cm.

2. A process according to claim 1, wherein the epoxy resin is adiepoxide of epichlororhydrin-bisphenol A condensate having epoxidegroups at both terminal positions of its molecular chain and having amolecular weight of about 360-560 and equivalent Weight based on epoxidegroups of about 180 to 260.

3. A process according to claim 1 wherein the amine hardener isdiethylenetriamine.

4. A process according to claim 1 wherein the abrasive grains areselected from the group consisting of Alundu-m, Carborundum and mixturesthereof.

5. A process according to claim 4 wherein the alundum and corrundum areemployed in admixture in the ratio of to Alundum to 30 to 40%Carborundum.

6. A grindstone produced by the process of claim 1.

References Cited UNITED STATES PATENTS 2,448,985 9/1948 Kuzmick 51-2982,462,480 2/1949 Eppler 51308 2,779,668 1/ 1957 Daniels 5l-298 3,020,1402/1962 Bluth 51-308 DONALD J. ARNOLD, Primary Examiner UJS. Cl. X.R.

